Method for near net shape manufacturing of high-temperature resistant engine components

ABSTRACT

For near net shape manufacturing of a high-temperature resistant component of complex design a high melting-point part of an intermetallic phase provided as a metal powder is mixed with a binder, and from the feedstock such formed a green compact substantially matching the final contour is produced by metal injection moulding, into the pores of said compact that remain after removal of the binder the low melting-point part of the intermetallic phase is infiltrated. The brown compact thereby created is mechanically processed, if required, and subjected to a specific heat treatment depending on the metallic phases used in order to create the intermetallic phase. This permits engine components consisting of intermetallic phases and having a geometrically complex structure to be manufactured cost-efficiently.

This invention relates to a method for near net shape manufacturing ofhigh-temperature resistant engine components of geometrically complexstructure by metal injection moulding.

A known method for near net shape manufacturing of components ofgeometrically complex design is metal injection moulding, also referredto as MIM. In metal injection moulding first a metal powder is mixedwith a binder including thermoplastics and waxes to form a flowingmaterial (feedstock) which is injected into a mould using an extruder ina conventional injection moulding process. After cooling, solidificationand demoulding, a so-called green compact is created, from which thebinder is removed thermally or chemically to provide a porous mouldedpart, the so-called brown compact. In a subsequent sintering process theporous brown compact is compacted into its final shape and has, due toits minor residual porosity, strength properties matching the propertiesof the solid material. In order to enable near net shape production alsoof high-temperature resistant engine components, e.g. turbine blades,the proposal has already been made to produce a powder consisting of anintermetallic phase and to use this powder in the manner described abovefor metal injection moulding. The manufacture of intermetallic phasesand of a powder made therefrom for metal injection moulding howeverinvolves high manufacturing effort and costs.

The object underlying the present invention is to provide acost-efficient method for near net shape manufacturing ofhigh-temperature resistant engine components of geometrically cornplexstructure.

It is a particular object of the present invention to provide solutionto the above problematics by a method in accordance with the features ofpatent claim 1.

Advantageous developments of the present invention become apparent fromthe sub-claims.

The basic idea of the invention is to mix a high melting-point part ofan intermetallic phase provided as a metal powder with a binder, and tocreate, by metal injection moulding, from the feedstock such formed agreen compact substantially matching the final contour, into the poresof said compact that remain after removal of the binder the lowmelting-point part of the intermetallic phase is infiltrated, with thebrown compact thereby created being subjected to a specific heattreatment depending on the metallic phases used in order to create theintermetallic phase.

This permits high-temperature resistant and lightweight enginecomponents of geometrically complex structure, such as for exampleturbine blades, to be manufactured cost-efficiently fromhigh-performance materials.

In an embodiment of the invention, a polymer two-component binder isused, where the first binder component is removed chemically,catalytically or thermally from the green compact created by metalinjection moulding, and the second binder component is removed thermallyduring infiltration of the low melting-point metallic part.

In a further embodiment of the invention, the proportion of the lowmelting-point part of the intermetallic phase is variable, beingdetermined by the proportion of pores after complete removal of thebinder from the green compact.

The proportion of pores and hence the proportion of the infiltrated lowmelting-point part in the intermetallic phase is determined by thesetting of the mixing ratio between the metal powder and thetwo-component binder.

In a further embodiment of the invention, infiltration of the molten andlow melting-point part of the intermetallic phase into the porous browncompact is performed under pressure using the squeeze casting method.

In a further embodiment of the invention, the brown compact can bemechanically processed after infiltration of the low melting-point partand before the heat treatment that creates the intermetallic phase.

An embodiment of the invention is described in more detail below inconjunction with the enclosed processing flow chart using the example ofmanufacture of a turbine blade consisting of an intermetallic phasebased on iron and aluminum.

An iron powder is manufactured from the high melting-point part of theintermetallic phase, in this case iron (step 1) and is mixed with apolymer binder including two components (step 2).

From the iron powder/binder mixture, the so-called feedstock—provided inthe form of a granulate—a green compact is produced using a screwextruder in a conventional injection process (step 3), from which greencompact the first component of the polymer binder is removed aftercooling, solidification and demoulding (step 4). The removal of thefirst component of the binder can be achieved chemically, catalyticallyand/or thermally. As a result of partial debindering, a porous browncompact consisting of the high melting-point metallic phase and thefirst component of the binder is obtained, which has a certain porosityadjustable depending on the binder proportion. In the following processstep, a low melting-point metallic phase—in this case aluminum—isinfiltrated in a modified die-casting process, so-called “squeezecasting”, into the cavities of the brown compact at high pressure,thermally removing the second component of the binder from the browncompact (step 5). The volume ratio between the high melting-pointmetallic phase (iron) and the low melting-point metallic phase(aluminum) is set using the respective porosity of the brown compact.After this step, mechanical processing of the infiltrated brown compact(step 6) can take place if necessary, which can be performed in a simplemanner at this point in time. Then the component matching the finalshape is subjected to a heat treatment (step 7) in order to form anintermetallic phase consisting of iron and aluminum, thereby providing ahigh-temperature resistant component of geometrically complex designmade by metal injection moulding, for example a turbine blade for agas-turbine engine.

In the same way, other high-temperature resistant and lightweightcomponents of geometrically complex structure can also be manufactured,efficiently and inexpensively with low expenditure on material, from anintermetallic phase, produced for example on the basis of nickel, iron,titanium and aluminum.

What is claimed is:
 1. Method for near net shape manufacturing ofhigh-temperature resistant engine components of geometrically complexstructure by metal injection moulding, the engine components consistingof an intermetallic phase of a high melting-point part and a lowmelting-point part, characterized in that the high melting-point partprovided as a metal powder is mixed with a binder, that a green compactof the engine component is first produced by metal injection moulding,that a porous brown compact is created after removal of the binder, thatsubsequently the low melting-point part of the intermetallic phase isinfiltrated into the pores of the brown compact in the molten state andthat finally the brown compact such prepared is subjected to a heattreatment generating the intermetallic phase.
 2. Method in accordancewith claim 1, characterized in that the proportion of the lowmelting-point part of the intermetallic phase is variable and isdetermined by the proportion of pores after complete removal of thebinder from the green compact.
 3. Method in accordance with claim 2,characterized in that the proportion of pores is determined by thesetting of the mixing ratio between the metal powder and thetwo-component binder.
 4. Method in accordance with claim 1,characterized in that the infiltration of the molten and lowmelting-point part of the intermetallic phase into the porous browncompact is performed under pressure using the squeeze casting method. 5.Method in accordance with claim 1, characterized in that the browncompact is mechanically processed after infiltration of the lowmelting-point part and before the heat treatment that creates theintermetallic phase.
 6. Method in accordance with claim 1, characterizedin that a polymer two-component binder is used, where the first bindercomponent is removed from the green compact created by metal injectionmoulding, and the second binder component is removed during infiltrationof the low melting-point part of the intermetallic phase.
 7. Method inaccordance with claim 1, characterized in that the first bindercomponent is removed chemically, catalytically and/or thermally, and thesecond binder component is removed thermally.